<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        ul{
            width: 300px;
            height: 400px;
            background: hsl(163, 96%, 50%);
        }
        li {
            background: darkorange;
        }
        /* li:first-child{
            background: seagreen;
        }
        li:last-child {
            background: mediumturquoise;
        }
        li:nth-child(3){
            background: moccasin;
        }*/
    
        li:nth-child(2n+1){
            background: yellow;
        }
        li:nth-child(2n){
            background: #05eb5d;
        }
    </style> 
</head>
<body>
    <ul>
        <li>1</li>
        <li>2</li>
        <li>3</li>
        <li>4</li>
        <li>5</li>
    </ul>
</body>
</html>